Not Applicable
1. Technical Field
This invention relates to outdoor lighting fixtures and more specifically to methods of maintaining clean light emitting surfaces or lenses on such devices.
2. Background Art
Luminaires, such as outdoor street lighting fixtures, are exposed to environmental pollution and dirt and dust. Many of these luminaires are not easily accessible for cleaning. In environments, classified as very dirty, a typical luminaire can lose 50% efficiency due to dirt within 24 months unless it is periodically cleaned. This loss of efficiency represents a large amount of wasted energy in the United States and other countries every year.
There is thus a need for the automatic cleaning of luminaires, such as outdoor street lighting fixtures.
The human eye maintains clean lenses by a constant fluid washing from the tear ducts. This approach, using a fluid wash in front of a lens, is not practical for luminaire lenses that have a long-term exposure ( greater than 1 year) to the environment without cleaning. My invention substitutes a plastic film over a lens for the same function that tears accomplish in the human eye.
An automatic plastic film feed device is placed in front of a light source. This plastic film is constantly moving, but at a very slow rate (xcx9c1 inch per month). Dirt and pollution from the environment are deposited on this plastic film instead of on lenses or other clear light emitting surfaces that are now placed in front of typical light sources.
The buildup of dirt on a lens from the environment is a fairly slow process and the lumen dirt depreciation factor (LDD) can be approximated by a formula provided in the Illumination Engineering Society of North America Lighting Handbook, 9th Edition as follows:
LDD=exe2x88x92[At]Bxe2x80x83xe2x80x83(Eq.1)
where A is a constant that represents the cleanliness of the environment and varies in a range from 0.038 to 0.396; B is a constant that represents the category of the luminaire and varies in a range from 0.53 to 0.88; and where t represents time in decimal years.
A lighting fixture in accordance with my invention is especially suitable for light areas where it either is inconvenient or impossible to change light sources or lenses, such as nuclear reactors or tunnels. Advantageously, this invention can be combined with a remote light source where light is provided to the apparatus via fiber optic cable, thereby allowing for the light source to be changed without access to the lighting enclosure required. Also advantageously, my invention can be powered by a spring-powered motor, such as is used in a clock or a child""s wind-up toy so that neither external power supply nor batteries, which are prone to chemical leakage, are required.